n=int(input())
c=list(input())

import math

rkosu=c.count("R")
wkosu=n-rkosu

ca=["R"]*rkosu+["W"]*wkosu

count=0
for i in range(n):
    if c[i] != ca[i]:
        count+=1

ans=math.ceil(count/2)
print(ans) n=int(input()) n int(input()) int input() input c=list(input()) c list(input()) list input() input import math math rkosu=c.count("R") rkosu c.count("R") c.count c count "R" wkosu=n-rkosu wkosu n-rkosu n rkosu ca=["R"]*rkosu+["W"]*wkosu ca ["R"]*rkosu+["W"]*wkosu ["R"]*rkosu ["R"] "R" rkosu ["W"]*wkosu ["W"] "W" wkosu count=0 count 0 for i in range(n):
    if c[i] != ca[i]:
        count+=1 i range(n) range n if c[i] != ca[i]:
        count+=1 c[i] != ca[i] c[i] c i ca[i] ca i count+=1 count 1 ans=math.ceil(count/2) ans math.ceil(count/2) math.ceil math ceil count/2 count 2 print(ans) print ans wkosu=n-rkosu n-rkosu wkosu count+=1 1 count ans=math.ceil(count/2) math.ceil(count/2) ans n=int(input()) int(input()) n count=0 0 count c=list(input()) list(input()) c ca=["R"]*rkosu+["W"]*wkosu ["R"]*rkosu+["W"]*wkosu ca rkosu=c.count("R") c.count("R") rkosu
n=int(input())
c=list(input())

import math

rkosu=c.count("R")
wkosu=n-rkosu

ca=["R"]*rkosu+["W"]*wkosu

count=0
for i in range(n):
    if c[i] != ca[i]:
        count+=1

ans=math.ceil(count/2)
print(ans)